The invention relates to an arrangement to stabilize two parallel coaxial lines, such as for example signal lines extending vertically and supported by a transmission tower.
It is known in antenna systems to have two parallel coaxial lines extending vertically upwards along the tower. These coaxial lines each include, for example, up to 2,000 feet of coaxial tubing in sections, forming a coaxial line fixed to the tower at the top of the line, so that the line is suspended from its top end.
Both coaxial lines may be suspended at points along their length by spring hangers from the tower to allow the coaxial lines to expand and contract with respect to the tower. The spring hangers provide stability while permitting vertical travel of the line relative to the tower due to factors such as thermal expansion of the line relative to the tower. Temperature variations produced by weather and the operating power of the coaxial line cause the coaxial lines to expand at a different rate than the tower. The coaxial line and the tower are also made of different materials, further contributing to differential expansion between the lines and the tower. For example, the coaxial line may be made of copper and the tower made of steel. Since these two metals have different coefficients of expansion, there is a differential in the thermal growth of the copper coaxial line with respect to the steel tower as temperature and power changes.
For this reason, it is known to suspend the coaxial lines from the top of the tower, so they are fixed both vertically and horizontally at the top of the coaxial line to the tower, but are essentially hanging in a suspended state from the top, with the lines being horizontally restrained by spring hangers that permit vertical movement along the length of the line. This permits the length of the line to have vertical travel, and the lower end of the coaxial lines, which usually terminate in an elbow connecting to a horizontal coaxial line section, are free to travel vertically relative to the tower.
A disadvantage of the known arrangement is that one of the two parallel coaxial lines may expand at a different rate than the adjacent coaxial line. For example, if one coaxial line is heated by the sun and the other coaxial line is in the shade, the first coaxial line will expand at a different rate than the second coaxial line. The differential in the relative linear expansion between two adjacent coaxial lines can cause a phase difference in the transmission of signals transmitted through the lines, which can result in undesirable beam tilt when the signal reaches the antenna. That is, if the two coaxial lines expand by different degrees along their length, the distance from the lower elbow to the fixed top portion of the line for each line will be a different total distance. Therefore, if one line elongates more than the other adjacent line, the effective and actual transmission length of the two lines will be different. Because these two lines are intended to carry signals that are at a fixed relative phase at the elbows in the lower portion of the lines, the change in length is undesirable because the signals at the top of the coaxial lines will become out of phase due to their having traveled a different distance.
Accordingly, there is a need for an arrangement that can tie together a pair of parallel coaxial lines and accommodate for differential expansion between sections of the adjacent lines while maintaining a constant relative total length between two points of the lines, such as for example, between a lower elbow and a fixed top end of each line.
It is therefore a feature and advantage of the present invention to provide an arrangement that can tie together a pair of parallel coaxial lines and accommodate for differential expansion between sections of the adjacent lines while maintaining a constant relative total length between two points of the lines, such as for example, between a lower elbow and a fixed top end of each line.
The above and other features and advantages are achieved through the use of a novel apparatus as herein disclosed. In accordance with one embodiment of the present invention, an apparatus is provided for stabilizing a pair of parallel coaxial runs in an antenna having a tower. An upper portion of each coaxial line is suspended from the tower, and a lower end of the coaxial lines is free to move vertically relative to the tower. The apparatus comprises a flexible section disposed along a portion of the length of one coaxial line and a frame which rigidly ties together the two coaxial lines at a portion of the lines below the flexible section.
In another aspect, the invention provides an apparatus as described above, where the portions of the lines which are tied together are elbows.
In yet another aspect of the invention, an apparatus is provided where the frame ties together the portions of the coaxial lines so that they are retained in a common horizontal plane.
In yet another aspect of the invention, the frame includes a cross member that is strapped to each of the second portions of the lines.
In still another aspect of the invention, an apparatus is provided where the frame further includes a stabilization assembly that surrounds the first coaxial line at a position above the flexible section and permits vertical travel of the coaxial line relative to the frame at the surrounded position, and inhibits lateral movement of the coaxial line at that position relative to the frame, thereby permitting the expandable element to expand and contract vertically, and inhibiting axial misalignment of the line above and below the flexible section.
Another aspect of the present invention relates to an apparatus having spring hangers each supporting one coaxial line from the tower so that the spring hangers permit vertical travel of the coaxial line relative to the tower and inhibit lateral movement of the coaxial line relative to the tower.
In accordance with another embodiment of the present invention, an apparatus is provided for stabilizing a pair of coaxial lines for an antenna having a tower, with an upper portion of each coaxial line being suspended from the tower, and a lower end of the coaxial lines free to move vertically relative to the tower. The apparatus has expanding means disposed along the first portion of one coaxial line, and tying means for rigidly tying together the two coaxial lines at a second portion of each of the lines below the expansion means.
In accordance with another embodiment of the present invention, a method is provided for stabilizing a pair of parallel coaxial lines in a tower. An upper portion of each coaxial line is suspended from the tower, and a lower end of the coaxial lines is free to move vertically relative to the tower. The method comprises the steps of providing an expandable element at a location between the upper portion and lower end of the coaxial line and holding the lower ends of the coaxial lines together at a relative horizontal height with each other.
In another aspect of the invention, the method includes the steps of permitting the lower ends to move vertically relative to the tower, while simultaneously holding the lower ends at the same height as each other.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract included below, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.